Analytical and experimental investigations have been completed which define the flow field in an apparatus designed to apply a controlled shear stress field to the endothelial surface of canine aorta in vitro. Permeability studies using Evans Blue Dye labelled albumin are in progress. Steady shear fields have been applied to the endothelial surface and changes in uptake of the tracer protein molecule are being measured. Mechanical proprties of the aorta wall are also being determined.